Bipolarins A-H, eight new ophiobolin-type sesterterpenes with antimicrobial activity from fungus Bipolaris sp. TJ403-B1

Bipolarins A-H ( 1-8 ), eight new tetracyclic ophiobolin-type sesterterpenes featuring a rare oxaspiro4.4nonane moiety, were isolated from cultures of fungus Bipolaris sp. TJ403-B1. Their structures and absolute configurations were elucidated by comprehensive spectroscopic analyses, single-crystal X-ray diffraction experiments, electronic circular dichroism and ¹³C NMR calculations. Additionally, compound 5 exhibited significant selective antimicrobial activity against Enterococcus faecalis with an MIC value 8 μg·mL^-1.